MacOSX resolvers can cache IPv4 addresses, making them preferable to IPv6-capable applications, such as web browsers. The apps are IPv6-capable, but if an IPv4 address is already cached for a given fully qualified domain name (FQDN), the apps can’t look up names properly to prefer IPv6 addresses when available. The fix is to manually clear your MacOSX DNS cache. Do that with the simple command:
sudo dscacheutil -flushcache
It’s called, cleverly enough, ipv6fw. Just type
man ip6fw
for the easy-to-follow 
instruction guide.
They can operate as a direct IPv6 gateway if your ISP supports IPv6, or it can operate as a tunneling device. To configure the tunneling option, follow these steps (courtesy of James Woodyatt):
1. Launch AirPort Utility.
2. Select your device from the sidebar and choose Manual Setup.
3. Select the [Internet] pane of the configuration window.
4. Select the TCP/IP tab.
5. At the “Configure IPv4″ pop-up, choose the “Manually” option.
6. Enter the statically assigned IPv4 WAN configuration parameters for your device:
+ IP Address
+ Subnet Mask
+ Router Address
+ DNS Servers
+ Domain Name [optional]
7. Select the [Advanced] pane of the configuration window.
8. Select the IPv6 tab.
9. At the “IPv6 Mode” pop-up, choose the “Tunnel” option.
10. At the “Configure IPv6″ pop-up, choose the “Manually” option.
11. Enter the statically assigned IPv6-in-IPv4 configuration parameters for your tunnel:
+ Remote IPv4 Address
+ Local IPv6 Address
+ Remote IPv6 Address
…also…
+ Enter the IPv6 address for a /64 LAN with a prefix that was assigned with your tunnel.
12. Click [Update] and wait for the AirPort/Time-Capsule to restart.
MacOSX uses the KAME project (http://www.kame.net) IPv6 protocol stack and tools.The KAME project was a joint effort of six companies in Japan to provide a free stack of IPv6, IPsec, and Mobile IPv6 for BSD variants. The project officially concluded in March 2006 and most of the components moved to FreeBSD, NetBSD, and MacOSX. Sometimes it’s helpful to see what the KAME version is in the MacOSX release you’re running. Here’s how:
sysctl -a | grep kame_version
net.inet6.ip6.kame_version: 20010528/apple-darwin
You can do this:
ssh root@2001:1234::1 (example address)
but you can’t do this:
scp root@2001:1234::1:/tmp/file .
because scp parses this as hostname 2001 and file path 1234::1:/etc/motd, yielding an error such as this one:
ssh: connect to host 2001 port 22: Connection refused
The scp manpage addresses this problem for -L and -R arguments (you can use the -6 option on scp to force all addresses to be interpreted as IPv6), but it is silent about using IPv6 when copying files.
The trick is to use square brackets to delimit the IPv6 address, which on the Mac also requires escaping the brackets, thusly:
scp root@\[2001:1234::1\]:/tmp/file .